Metal article



A. L. DAVIS METAL ARTICLE June 24, 1930.

Filed Nov. 18. 1925 specifically to such Patented June 24, 1 930 UNITED STATES PATENT OFFICE ALVAN L DAVIS, 01 WATERBURY, CONNECTICUT, ASSIGNOR TO SCQVILL MANUFAC- 'LURING COMPANY, OF WATERBURY, CONNECTICUT, A CQRPORATION F CONNECT- ICUT s Application filed November This invention relates to-certain improvements in metal articles comprising a stem hay'ing an enlarged head thereon, and more metal articles as cap screws or bolts. I

According to an approved practice of manufacturing cap screws or bolts, cold til drawn wire stock is upset to form a headed blank and the head of the blank is then shaped to be engaged by a tool, as for example, by cutting facets thereon. Cap screws or bolts so formed, however, are frequently characterized by a brittleness of the metal in the head which renders the head liable to break.

It is the object of the present invention to produce a metal article such as a bolt or cap screw, or, more generally speaking,an article consisting of a headed stem formed from cold drawn metal, such that this brittleness ofthe head is avoided.

\Vith this object in view, the invention consists in the article having the characteristicsherein described and specifically pointed out. a

Referring to the accompanying drawings,

Figure l diagrammatically represents, in section, a blank for a cap screw formed from a cold' drawn steel wire or rod having a head formed thereon by cold upsetting; and, Figure 2 diagrammatically represents, in sectioma completed cap screw made in accordance with the invention.

Referring to the drawings, 11 represents the stem of the blank which is formed from cold drawn rod or wire and 12 represents the head. The cold "drawing process has modified the original characteristics of the metal in the stem. the crystals having been somewhat elongated. In the natural condition of the metal and before the cold drawing process, the crystals in the metal from'which the .wire or rod is formed, are

substantially equiaxed, i. e. under the microscope, they'appear to be more or less cubical 111 f0ll11.- The cold drawing, however, tends to elongate the crystals or grains in the direction of the drawing, and this is repre sented in Figs. 1 and 2 by the character A stem which has the grains or crystals in METAL ARTICLE 18 1925. Serial No. 69,812.

this elongated condition is stronger, particularly as to tensile strength, than-is a* stem the metal in which has the crystals in normal condition.

Referring to Fig. 1, and-particularly to the head, as a result of the upsetting process the form of the crystals or major part of the head has so that the crystals are flattened, the metal crystals presenting a sortof laminated or schistose structure which is indicated'in Fig. l by the character The structure of the grains in the been changed stem extends somewhat up into the head, as

by this laminated 'or schistose converted into this laminated-0r schistose condition with the result that thehead is brittle and is liable to-break in use.

Referring to Fig. 2, the completed cap screw comprises the stem 13 and head 14. In this completed cap screw. of the present invention the bulk metal in the head Mare recrystallized so that they more nearly approach an equiaxed condition. As a result the,head' is tough and not brittle. This condition is indicated by the character 0. l

In forming this novel article, the head is subjected to an annealing process which should be conducted in such a way that the metal in the head is'substantially annealed of the grains in the before suflicientheat is conducted from the head into the stem to change the character istics of the metal in the stem. This annealing may be accomplished by subjecting the head of the bolt to a lead bath as described in my companion application Serial N o.

v 69,813, filedof even date herewith, or it may Bennett, Serial about in diameter and a head about thereon, the temperature to which the head is raised will vary-according to the character of the metal but will be sufficient to relieve the stresses and strains which have been set up in the metal by the cold upsetting. The temperature will usually vary within what is known as the annealing range, that is, from around 1300 F. to around 1700 F. In annealing by a lead bath'the head may be lowered into the bath until about of the head is immersed and retained until the head is given a red heat without raising the remainder of the blank beyond a black heat. The bath should be at such a temperature and the blank should be immersed for such a period of time that the head will be heated to a temperature within the annealing range referred to with out sufficient heat being conducted to the stem to change substantially its characteristics.

As disclosed in the Bennett application referred to, for a bolt blank having a stem I! in diameter, a three-phase current having a voltage between electrodes of 1.3 and a current of 1100 amperes per phase. has been found suitable, the time of heating being approximately three seconds.

The result of this annealing process is to recrystallize the bulk of" the grains in the metal in the head so that they are no longer in a laminated or schistose condition but more nearly approach an equiayed condi-' tion. This annealing or recrystallization of the grains strengthens or toughens the head and removes the condition-of brittlenes's' here the completed cap screw of the invention is further shaped by cold working, as for instance, where facets have been formed. thereon, the metal in the surface of the'facets, and, to some extent behind this surface, has its grains or crystals elongated to approach the condition of the metal in the stem. This shaping may be accomplished, for example, by the drawing operation described in my companion application,

Serial No. 69,813, filed of even date herewith. This condition of reconversion or reto by a wrench or other tool used in driving by the character X.

The result of the various operations which have been described is the production of a cap screw or similar article having a strong stem, a tough head and facets (or. other outer surface) of such characteristics that they will withstand, without deformation, any ordinary amount of force applied thereto by a wrench or other tool used in driving the screw home.

The method of producing the article herein described is claimed in the said com panion application, Serial No. 69,813.

lVhat I-claim is: l. A cap screw or bolt having a faceted head and a stem, the crystalline structure of the metal inthe stem being modified so thatsome or all of the crystals are somewhat elongated whereby the strength of the stem is increased, the metal in and behind the facets of the head having somewhat the characteristics of the metal in the stem, and the bulk of the metal in the interior of the head being-in the recrystallized condition characteristic of annealed metal.

2. A cap screw or bolt having a faceted head, the metal in the stem and in the facets having its crystals in the elongated conditionproduced by working cold, the bulk of the metal in the interior of the head having its crystalline structure in the condition produced by annealing.

3. A cap screw or bolt, the crystalline structure of the metal in the stenrbeing modified so that some or all of the cistals are somewhat elongated whereby the strength of the stemis increased, the metal in and behind the surface of the head having somewhat the characteristics of the metal in the stem and the bulk of the metal in the interior of the head being in the recrystallized condition characteristic of annealed metal.

In testimony whereof, I have hereunto set. ,my hand.

ALVA): L. DAVIS.

5 CERTIFICATE OF CORRECTION. Patent No. 1,767,653. Granted June 24, 1930, {0

ALVAN L. DAVIS. I

It is hereby certified that error appears in the printed specification oi the above numbered patent requiring correction as follows: Page 2, lines 49 and 50, strike out the words "or reto by a wrench or other tool used in driving" and insert instead of recrystallization is indicated in the drawing; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 2nd day of September, A. D. 1930.

- M. J. Moore, (Seal) Acting Commissioner of Patents. 

